Battery selector and charging

[Sven]

In anticipation of getting back down to the boat this weekend and tackling the alternator question I've been reading the 12-volt bible for boats.

One thing that surprises me is that he seems to imply that the battery selector has to be set to "both" for both batteries to charge. Looking at the wiring diagram he provided doesn't really help but I assume I must be reading him wrong ? Are any boats' battery banks really wired so that all the batteries don't get charged (by the AC charger at dockside) if the battery selector is set to just one bank ?

Maybe he is saying that under power the alternator will not charge both batteries unless the selector is set to both, but even that seems odd as you would have to remember to manually turn the selector to both to charge and then remember to turn on only the house bank once you stop the engine (or risk drawing down all batteries).



-Sven

 

[Emerald]

Indeed, the selector switch will determine which battery (or both) gets the charge from running the engine. However, the AC based charger should be independent, and the few I've seen have all been set to charge both batteries simultaneously.

 

[u079721]

Electrical systems are right up there with guns and anchors as being topics sailors seem to like to discuss.

For the engine alternator, the classic set up was indeed to run the output to the battery switch, and you then had to choose A, or B, or Both.

But the dockside battery charger is a separate issue. Typically these are wired directly to the batteries themselves, and charge independently of where the battery switch is set. But since you don't know how your particular unit was installed, it would be a good idea to trace the wiring to both familiarize yourself with your system, and to be sure it is done correctly.

Good luck!

 

[Sven]

David and Steve,

Thanks, interesting !

I would have assumed that the alternator output would run into a charger that acted like an AC charger, intelligently splitting the charging as needed for each of two banks. Boy was I wrong.

Given your explanations and the 12-volt bible, that must mean that if are set to "both" and you have one charged and one discharged bank, the charged bank will get overcharged until the discharged bank is also charged ? That doesn't sound like a very good way of prolonging battery life

Thanks again,


-Sven

 

[gareth harris]

The solution would appear to be to use the switch to charge the batteries as you want them, except that I once read that even the momentary removal of load on the alternator while the switch is changed can damage the voltage regulator. I am sure I have done exactly that any number of times, without damage, and would be interested to know if anyone has fried a regulator that way.

My quick fix was to wire the alternator directly to the house battery, and only charge the starting battery from shore power - cranking the engine does not use a lot of charge unless you have major engine problems.

If you have the time and inclination, you can wire the system any way you like; and if you have the money you can find smart charging options of the type you describe.

gareth
Freyja E35 #241 1972

 

[Emerald]

that must mean that if are set to "both" and you have one charged and one discharged bank, the charged bank will get overcharged until the discharged bank is also charged ?

At first I was going to write, nope, that's where your regulator comes in, but you have an odd scenario where one battery is down and one up and they've not been kept charged up. So, possibly yes, but if you switch between the two, the regulator should stop putting charge to the battery once it is at capacity (float). Now, that other battery will remain discharged until you switch over to it, whereupon the regulator will sense it requires charging, and it will do so. Going back to the old addage that electricity flows to least resistance, I have a couple gut reactions to running one up and one down in the both switch position. First, the two batteries are going to somewhat balance out. The low battery will pull down the more charged battery. Also, the current from the alternator should really go to the battery requiring more charge - path of least resistance. So, I think while it may not charge as efficiently, you would not overcharge the good battery by running in both while the low battery works its way up. Again, switching over to the one battery in need of charge will get you charged up quicker.

To answer Gareth's concern on switching while running, it's a mixed answer. To the best of my knowledge, all marine battery switches with 1/both/2 settings will let you switch between any of the three positions 1/both/2 without harming the diodes in your alternator. This is because they are "make before break" switches. When you move from one position to another, the new position is engaged (switched on) before the old position is disengaged. If you were to turn the switch to the OFF position is when you run into problems. There are special battery switches that will protect your diodes if you make a mistake, but don't assume you have it unless you installed it

Of note, I am sure I've mistakenly hit the off position at least once, and not blown my diodes. It was a very brief mistake, and I seemed to survive, but I would not recommend trying it out

 

[Sven]

if you have the money you can find smart charging options of the type you describe.

More googling coming up ... not because the money is there but because it seems like it might be cheaper in the long run

At first I was going to write, nope, that's where your regulator comes in, but you have an odd scenario where one battery is down and one up and they've not been kept charged up.

If you stay on the hook for a few days or a week or are sailing during a crossing the house bank would likely get run down while the starting battery stays more or less topped up, ready to crank when the engine is finally needed.

"make before break" switches.

I looked at the OEM selector switch to see if it specifically said make-before-break but didn't see it. I suspect it is m-b-b but didn't want to take any chances.

Thanks for all the insights,


-Sven

 

[Tom Metzger]

I looked at the OEM selector switch to see if it specifically said make-before-break but didn't see it. I suspect it is m-b-b but didn't want to take any chances.

Sven - Note the order of the switch positions: 1-Both-2. This means that the switch goes from a single contact to shorting both together before going to the other single contact. It does make contact before breaking contact.

You have picked up the obvious truth that there is no benefit in always charging both batteries if you are only using one. I strongly believe in Gareth's method of charging (charge the starting battery only with shore power) for the reason he mentions. I, along with many others, don't normally start the engine with the starting battery. It's just there for backup. I recommend not installing "smart" schemes to automatically charge the starting battery. Combiners, Echo chargers, and the like are just that much more hair in the scuppers as far as I am concerned.

 

[u079721]

Sven - Note the order of the switch positions: 1-Both-2. This means that the switch goes from a single contact to shorting both together before going to the other single contact. It does make contact before breaking contact.

You have picked up the obvious truth that there is no benefit in always charging both batteries if you are only using one. I strongly believe in Gareth's method of charging (charge the starting battery only with shore power) for the reason he mentions. I, along with many others, don't normally start the engine with the starting battery. It's just there for backup. I recommend not installing "smart" schemes to automatically charge the starting battery. Combiners, Echo chargers, and the like are just that much more hair in the scuppers as far as I am concerned.

Agreed. I inherited a system with a big house bank, a starting battery, and on-off switches for each. At the dock everything was charged by the AC battery charger, but when cruising only the batteries turned ON would be charged by the alternator. So I purchased a battery combiner so I could leave the back up battery turned OFF yet still have it receive a charge while motoring, and used the house bank for everything including starting the engine. But then I worried about overcharging the mostly topped off starting battery, and tried disconnected the combiner. I found that if I started a month long cruise with a topped off starting battery, it was still going strong as a reserve after a month of sitting there. After that I didn't worry any more about charging the reserve battery, and just left the house bank ON all the time while cruising, and left the back up battery OFF. That way I avoided any confusion about whether I had switched the system from A to B or Both or whatever. Once I left the dock I just didn't touch the switches at all.

For this to work I had to have a single house bank, wired in parallel, which I was OK with, but which some folks think is unwise. And if I had been out for more than a month I would have made a point of topping off the back up battery at least once. But the way I used it the system was hands off and trouble free.

But remember, if there are N sailors in a discussion, there will be at least N+1 different ways to set up the electrical systems. You just have to find a system that works for you the way you use your boat.

 

[Emerald]

But remember, if there are N sailors in a discussion, there will be at least N+1 different ways to set up the electrical systems. You just have to find a system that works for you the way you use your boat.

How true, and I was thinking earlier about how easy it is for folks to get caught up in the technology so to speak, and loose sight of the goals at hand. I have an original style system with a modern 3 stage charger for dockside. The prior owner switched to hybrid deep cycle/starting batteries. I predominantly day sail with scattered overnights. I couldn't make the system any simpler, and for this type of use, I wouldn't change a thing. A year or so ago I helped a fellow sort out all sorts of self inflicted issues from deciding he wanted to upgrade his system to AGM batteries and have a multi-battery house bank and a separate starting battery. No refrigeration or other electrical demands outside of a few instruments and running lights. Not sure if the boat ever left the slip for more than a few hours at a time. Never could figure out why he thought he needed what he got himself into other than it was the thing to do because it was the current technology. I'd rather buy a new sail

 

[gareth harris]

If you stay on the hook for a few days or a week or are sailing during a crossing the house bank would likely get run down while the starting battery stays more or less topped up, ready to crank when the engine is finally needed.

-Sven

If you are preparing the boat for cruising, the book I always recommend is Nigel Calder, who explains building a system very thoroughly. WRT technology, motor boaters tend to have far more elaborate systems since they have charging capacity galore and owners with enough money they usually do not like to forgo landlubber luxuries, so keep that in mind as you look through google.

As I started to set up Freyja for cruising, I made space for one 4D alongside the engine, and one emergency start battery, with the selector switch buried in the compartment so it could not be inadvertently changed. I then made sure that my normal power demands in 24hrs would not exceed 30% of the rated capacity of the 4D, to stay within the optimum 50% - 80% state of charge, and then installed 30A smart charging capability which is as much as is useful for one 4D, and could do the bulk of recharging in a little over an hour. It was a nice simple system with limited expensive components.

With an E39, your power demands will likely be higher, depending on the number of crew you want to be able to take and their taste for minimalism (how many of them will be women?), so design your own system (perhaps based around and 8D?) but my personal view is I think there is some benefit in not having one of the fully automated battery regulating and switching systems, in that it keeps the skipper more aware of what state his electrical system is in.

Gareth
Freyja E35 #241 1972

 

[Tom Metzger]

Very important

...so design your own system (perhaps based around an 8D?)...

When choosing batteries keep in mind whose back will be lifting and installing them.

 

[Sven]

Hi Gareth,

I think there is some benefit in not having one of the fully automated battery regulating and switching systems, in that it keeps the skipper more aware of what state his electrical system is in.

Your point(s) and others in this thread are very important and relevant to any system engineering challenge. The manual vs. autonomous/automatic trade-offs near and dear to me personally but that's a very long different story

Calder raises similar points in his diesel book. He points out that modern high tech diesels are marvels of efficiency and reliability but that the advances are due to electronic technology which if it fails could leave you much more stranded than an old "simple" diesel would. He also suggests that the "limp-home" capability should be part of the evaluation when choosing a new engine. (I would never call a diesel simple after reading his book ... they are amazing machines, both in precision tolerance and in the complexity of all the various design options).

Back to the electrical system. If truly on your own KISS certainly has many advantages over fully automated, even if the automation is there to increase reliability. Even if the automated system is more reliable than the KISS system, when something does go wrong, is it possible for the crew to figure out what is wrong and do something about it ? Does the system degrade gracefully or catastrophically and are there back-up options ?

If it is KISS, I want to make sure that really stands for "keep it simple stupid" and not "keep it stupidly simple".

I am still trying to understand the various options and appreciate all the opinions and info.


-Sven

 

[jmcpeak]

I have no relationship with Blue Sea Systems but this is what I bought to solve the charging issue that was brought up at the very beginning of this thread.
http://bluesea.com/products/7610. Not only does it allow for charging of both batteries regardless of the switch separation, it "protects sensitive electronics by temporary isolation of house loads from engine circuit during engine cranking".

Have fun,

Jason

 

[rwthomas1]

Everyone has opinions about what works and here is mine:

The alternator is wired directly to the house battery. That way there is no way of inadvertently switching the battery switch to OFF and frying diodes. The switch I use is: http://bluesea.com/products/5511e
This switch connects the house battery with house loads, ie. the DC panel AND it connects the start battery to the starter. This occurs in parallel. The start battery ALWAYS starts the engine and the house bank ALWAYS assumes house loads. You will note a "combine" position on the Blue Seas switch. This allows the engine to be started by the house or the start battery to run the house loads if needed. Its very simple and works very well. I have never understood the point of having an unused start battery sitting there. Using it to start the engine regularly is a good thing.

The start battery is charged by the alternator AND shore power charger through this product. http://bluesea.com/products/7600
This device charges the start battery by automatically paralleling the house and start batteries once the charging voltage reaches a selectable low point and disconnects at a selectable high point. Both the alternator and shore charger are wired directly to the house bank and the BatteryLink doesn't care where the charge current originates, it just does its job.

Some may see this system as complex. It really isn't There is only one extra piece involved, the BatteryLink, over a "normal" system. It automates the battery charging process and makes it dummy proof. At any point the system can be over-ridden with the battery switch. The BatteryLink can be easily disabled by removing a fuse.

I'm on a mooring. I don't have the luxury of shore power to keep my batteries, start or otherwise, topped off. The alternator/regulator/etc. on my boat is intended to stand alone, recharge the banks, etc. without ever being plugged in. Likely overkill to some but peace of mind to me.

Works for me. RT

 

[Sven]

To the best of my knowledge, all marine battery switches with 1/both/2 settings will let you switch between any of the three positions 1/both/2 without harming the diodes in your alternator. This is because they are "make before break" switches. When you move from one position to another, the new position is engaged (switched on) before the old position is disengaged.

It is probably a good idea to use the switch every now and then. I don't know if Lew ever changed the setting but we hadn't since we first took possession. Surprise, when I first changed from one battery to both and then the other (not under power) I got the distinct GPS boot-up beep and the iPod paused. I assume there must have been corrosion on the switch surface that broke the connection long enough for the electronics to notice.

I could not repeat the disconnect so I think just using the switch got rid of whatever caused it.


-Sven

 

[Mort Fligelman]

Blue Sea ACR

Sven:

I attended a talk by Nigel Calder just over 2 years ago.......

At that time he went through all of the relative advantages of using an Automatic Charging Relay (ACR) as Rob Thomas Describes.

After that, I read about this in an issue of Sailing Magazine......The magazine with this article is on my desk in Illinois (I Know....what the H--- good is it doing us there), but it expounded further on the merits of the ACR, and the combiner switch.....

I put this system in my boat along with 3 #27 90AH Batterys.......I have been most happy with it......I run my refrigeration for several hours, and burn lights like crazy when overnight.......electric power is not one of my worries....

I am not an engineer by any stretch.......just a boy builder with limited knowledge, but I ask a lot of questions from my knowledgeable friends, and all of them agreed that this system looked pretty much bullet proof.....

FWIW

 

[Tom Metzger]

After that, I read about this in an issue of Sailing Magazine......

What a surprise! :thinker: A magazine, dependent on advertising, advocating using additional products.

YMMV

 

[u079721]

Well as I mentioned above, after awhile I disconnected the battery combiner (ACR) from my system, because I didn't really need it as I was only away from the dock (and shorepower) for a month at a time. If you were cruising full time you would need to either remember to charge the back-up battery from time to time, or hook up an ACR to have it done automatically. It seems as if much of the complexity that we get into with these systems is in an attempt to make everything fool proof and hands off. That's great, but it does come at a cost!